System and method for person or object position location utilizing impulse radio

ABSTRACT

A System and Method for Person or Object Position Location Utilizing Impulse Radio, comprising a plurality of reference impulse radios; an object or person to be tracked having a mobile impulse radio associated therewith; an architecture with an associated positioning algorithm associated with said plurality of impulse radio reference radios and said mobile impulse radio; and display means for displaying the position of the person or object whose position is to be determined.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 10/298,334 entitled “System and Method for Person or ObjectPosition Location Utilizing Impulse Radio” filed Nov. 18, 2002, now U.S.Pat. No. 7,397,379 which is a continuation of Ser. No. 09/710,555 filedon Nov. 10, 2000 now U.S. Pat. No. 6,501,393 issued Dec. 31, 2002, whichis a continuation-in-part of Ser. No. 09/407,106 filed on Sep. 27, 1999now U.S. Pat. No. 6,512,455 issued Jan. 28, 2003 and acontinuation-in-part of Ser. No. 09/456,409 filed on Dec. 8, 1999 nowU.S. Pat. No. 6,300,903 issued Oct. 9, 2001, which is acontinuation-in-part of Ser. No. 09/045,929 filed on Mar. 23, 1998 nowU.S. Pat. No. 6,133,876 issued Oct. 17, 2000, all of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to positioning systems andmethods. More particularly, the present invention provides person orobject positioning in a predetermined area.

2. Background of the Invention and Related Art

The ability to ascertain the location of an individual or object occursin countless scenarios. One such scenario includes emergency situationswhere an emergency worker is in a building wherein potential dangerlies. An example of this is a firefighter fighting a fire inside aburning building. It would be very beneficial and potentially lifesaving to be able to track the movements and current location of afirefighter inside a burning building. Also, it would be veryadvantageous to be able to transmit information relating to the personwhose location is being tracked and surrounding environment whichsurrounds them. This would be an example of a scenario wherein thelocating area varies.

In the firefighter example, the location would vary depending on wherethe fire may be located. However, in numerous positioning embodimentsthe objects or persons whose position is to be determined are located ina fixed area for at least a given period of time. In this scenario theobject or person may be moving within a given defined area and its/theirposition is desired to be located. An example of this may includetracking a prison guard inside of a prison. Danger is inherent in aprison environment and knowing where prison guards are within theconfines of a prison is vital. An additional benefit would be to notonly be able to know the location of a prison guard, but also to enablethe prison guard to communicate on the same device that is tracking hislocation. Furthermore, the ability to provide an emergency notificationwould be beneficial. Consequently, if one mobile unit could providecommunication, alerting and positioning, the benefits to prison guardswould be enormous.

Another example of a person or object moving within a defined area is achild in a theme park such as Disney World in Orlando, Fla. Thisenvironment typically includes family members with children. Hundreds ofchildren are lost in Disney World each year as children wander off ifthe parents turn their head for even a brief period. This can be a verydangerous situation and there is an immense need to be able to find thelost child's exact position immediately. With thousands of people and alarge geographic area, this is a difficult task.

Another important task is to know the position of items in a warehouse.Billions of dollars are spent each year on shipping items from onelocation to another. Many times these items are stored in severallocations prior to its arrival at the final destination. In a priorapplication, filed by the present inventor, application Ser. No.09/407,106, filed Sep. 27, 1999, entitled “System and Method forMonitoring Assets, Objects, People and Animals Utilizing Impulse Radio”,now U.S. Pat. No. 6,512,455, issued Jan. 28, 2003, a method of trackingsuch items utilizing impulse radio was described and is incorporatedherein by reference. However, positioning architectures in thatapplication were not used to determine the exact location of itemswithin a warehouse or other area.

Further, numerous other techniques, both completely wireless andpartially non-wireless, have been attempted for position locating withlimited success. The reason for this limited success is the inherent RFproperties of existing technologies. In the burning building example,severe multipath problems exist as well as an extremely noisy RFenvironment is present. The RF environment is cluttered with emergencyradio signals from police and firemen as well as hand held radios fromfiremen working on the fire. Most buildings are filled with multipathpropagation problems and are inherently unreliable in that environment;and a fireman in a burning building is a situation that requires extremereliability.

In areas such as the Disney World example, attempts have been made to beable to locate people and objects, but again with limited success. Themetal rides, the large buildings and many other multipath causing thingsare present. Thus, a child may be in between two large buildings andunder a metal picnic table, cowering in fear for having lost hisparents, and conventional radios may not be able to find his position.Further, power and component requirements for conventional wirelesstechnology make placing transmitters with each child problematic due tothe size, expense and limited battery life of the transmitters.Therefore, there is a strong need for a wireless position locatingsystem that has advantageous multipath propagation properties, has lowtransmit power and can be mobile if needed. Also, there is a need for awireless locating system that, due to it's inherent properties, can beimplemented with a large number of varying architectures.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a positionlocating system and method utilizing impulse radio techniques.

It is another object of the present invention to provide a positionlocating system and method utilizing impulse radio that can be mobile orfixed.

It is a further object of the present invention to provide a positionlocating system and method utilizing impulse radio with the ability toimplement a variety of positioning architectures depending on the needsof the system and method.

These and other objects are provided, according to the presentinvention, by a plurality of impulse radio reference radios; an objector person to be tracked having a mobile impulse radio associatedtherewith; an architecture with an associated positioning algorithmassociated with said plurality of impulse radio reference radios andsaid mobile impulse radio; and display means for displaying the positionof the person or object whose position is to be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1A illustrates a representative Gaussian Monocycle waveform in thetime domain;

FIG. 1B illustrates the frequency domain amplitude of the GaussianMonocycle of FIG. 1A;

FIG. 2A illustrates a pulse train comprising pulses as in FIG. 1A;

FIG. 2B illustrates the frequency domain amplitude of the waveform ofFIG. 2A;

FIG. 3 illustrates the frequency domain amplitude of a sequence of timecoded pulses;

FIG. 4 illustrates a typical received signal and interference signal;

FIG. 5A illustrates a typical geometrical configuration giving rise tomultipath received signals;

FIG. 5B illustrates exemplary multipath signals in the time domain;

FIGS. 5C-5E illustrate a signal plot of various multipath environments.

FIG. 5F illustrates the Rayleigh fading curve associated withnon-impulse radio transmissions in a multipath environment.

FIG. 5G illustrates a plurality of multipaths with a plurality ofreflectors from a transmitter to a receiver.

FIG. 5H graphically represents signal strength as volts vs. time in adirect path and multipath environment.

FIG. 6 illustrates a representative impulse radio transmitter functionaldiagram;

FIG. 7 illustrates a representative impulse radio receiver functionaldiagram;

FIG. 8A illustrates a representative received pulse signal at the inputto the correlator;

FIG. 8B illustrates a sequence of representative impulse signals in thecorrelation process;

FIG. 9 illustrates the potential locus of results as a function of thevarious potential template time positions;

FIG. 9A illustrates four nodes in an Impulse Radio TDMA linked networkand the known distances between each node.

FIG. 9B illustrates the four time slots associated with a four nodeImpulse Radio TDMA network.

FIG. 10 is an example of a full duplex positioning architecture withsynchronized transceiver tracking.

FIG. 11 is an example of a full duplex positioning architecture withunsynchronized transceiver tracking.

FIG. 12 is an example of a transmitter positioning architecture withsynchronized transmitter tracking.

FIG. 13 is an example of a transmitter positioning architecture withunsynchronized transmitter tracking.

FIG. 14 is an example of a receiver positioning architecture withsynchronized receiver tracking.

FIG. 15 is an example of a receiver positioning architecture withunsynchronized receiver tracking.

FIG. 16 is an example of a mixed mode positioning architecture withmixed mode referenced radios.

FIG. 17 is an example of a mixed mode positioning architecture withmixed mode mobile radios.

FIG. 18 is an example of a specialized antenna architecture withsteerable null antennae designs.

FIG. 19 is an example of a specialized antenna architecture withdifferent antennae designs.

FIG. 20 is an example of a specialized antenna architecture withdirectional antennae designs.

FIG. 21 is an example of amplitude tracking architectures with amplitudesensing tracking.

FIG. 22 is an example of navigation augmentation architectures with GPSaugmentation.

FIG. 23 is an example of navigation augmentation architectures withGPS/INS augmentation.

FIG. 24 is an example of navigation augmentation architectures withgeneric navigation sensor augmentation.

FIG. 25 illustrates impulse radio mobile positioning wherein theposition of firefighters within a building are determined.

FIG. 26 is a block diagram illustrating the components in the impulseradio mobile positioning system and method of FIG. 25.

FIG. 27 illustrates the impulse radio fixed positioning system whereinthe location of a child in a theme park is depicted.

FIG. 28 is a flow chart of the process involved with the method oflocating the position of a lost child in a theme park that is equippedwith a system and method for position location using impulse radio.

FIG. 29 illustrates the impulse radio fixed positioning system whereinthe location of cargo in a warehouse is located.

FIG. 30 is a block diagram illustrating the components in the impulseradio fixed positioning system and method as used in the cargo andwarehouse example.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Overview of the Invention

The present invention will now be described more fully in detail withreference to the accompanying drawings, in which the preferredembodiments of the invention are shown. This invention should not,however, be construed as limited to the embodiments set forth herein;rather, they are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of the invention to thoseskilled in art. Like numbers refer to like elements throughout.

Recent advances in communications technology have enabled an emerging,revolutionary ultra wideband technology (UWB) called impulse radiocommunications systems (hereinafter called impulse radio). To betterunderstand the benefits of impulse radio to the present invention, thefollowing review of impulse radio follows. Impulse radio was first fullydescribed in a series of patents, including U.S. Pat. Nos. 4,641,317(issued Feb. 3, 1987), 4,813,057 (issued Mar. 14, 1989), 4,979,186(issued Dec. 18, 1990) and 5,363,108 (issued Nov. 8, 1994) to Larry W.Fullerton. A second generation of impulse radio patents include U.S.Pat. Nos. 5,677,927 (issued Oct. 14, 1997), 5,687,169 (issued Nov. 11,1997) and 5,832,035 (issued Nov. 3, 1998) to Fullerton et al. Thesepatent documents are incorporated herein by reference.

Uses of impulse radio systems are described in U.S. patent applicationSer. No. 09/332,502, entitled, “System and Method for IntrusionDetection Using a Time Domain Radar Array,”, now U.S. Pat. No.6,177,903, issued Jan. 23, 2001, and U.S. patent application Ser. No.09/332,503, entitled, “Wide Area Time Domain Radar Array,” now U.S. Pat.No. 6,218,979, issued Apr. 17, 2001, both filed on Jun. 14, 1999 andboth of which are assigned to the assignee of the present invention.These patent documents are incorporated herein by reference.

Impulse Radio Basics

This section is directed to technology basics and provides the readerwith an introduction to impulse radio concepts, as well as otherrelevant aspects of communications theory. This section includessubsections relating to waveforms, pulse trains, coding for energysmoothing and channelization, modulation, reception and demodulation,interference resistance, processing gain, capacity, multipath andpropagation, distance measurement, and qualitative and quantitativecharacteristics of these concepts. It should be understood that thissection is provided to assist the reader with understanding the presentinvention, and should not be used to limit the scope of the presentinvention.

Impulse radio refers to a radio system based on short, low duty cyclepulses. An ideal impulse radio waveform is a short Gaussian monocycle.As the name suggests, this waveform attempts to approach one cycle ofradio frequency (RF) energy at a desired center frequency. Due toimplementation and other spectral limitations, this waveform may bealtered significantly in practice for a given application. Mostwaveforms with enough bandwidth approximate a Gaussian shape to a usefuldegree.

Impulse radio can use many types of modulation, including AM, time shift(also referred to as pulse position) and M-ary versions. The time shiftmethod has simplicity and power output advantages that make itdesirable. In this document, the time shift method is used as anillustrative example.

In impulse radio communications, the pulse-to-pulse interval can bevaried on a pulse-by-pulse basis by two components: an informationcomponent and a pseudo-random code component. Generally, conventionalspread spectrum systems make use of pseudo-random codes to spread thenormally narrow band information signal over a relatively wide band offrequencies. A conventional spread spectrum receiver correlates thesesignals to retrieve the original information signal. Unlike conventionalspread spectrum systems, the pseudo-random code for impulse radiocommunications is not necessary for energy spreading because themonocycle pulses themselves have an inherently wide bandwidth. Instead,the pseudo-random code is used for channelization, energy smoothing inthe frequency domain, resistance to interference, and reducing theinterference potential to nearby receivers.

The impulse radio receiver is typically a direct conversion receiverwith a cross correlator front end in which the front end coherentlyconverts an electromagnetic pulse train of monocycle pulses to abaseband signal in a single stage. The baseband signal is the basicinformation signal for the impulse radio communications system. It isoften found desirable to include a subcarrier with the baseband signalto help reduce the effects of amplifier drift and low frequency noise.The subcarrier that is typically implemented alternately reversesmodulation according to a known pattern at a rate faster than the datarate. This same pattern is used to reverse the process and restore theoriginal data pattern just before detection. This method permitsalternating current (AC) coupling of stages, or equivalent signalprocessing to eliminate direct current (DC) drift and errors from thedetection process. This method is described in detail in U.S. Pat. No.5,677,927 to Fullerton et al.

In impulse radio communications utilizing time shift modulation, eachdata bit typically time position modulates many pulses of the periodictiming signal. This yields a modulated, coded timing signal thatcomprises a train of identically shaped pulses for each single data bit.The impulse radio receiver integrates multiple pulses to recover thetransmitted information.

Waveforms

Impulse radio refers to a radio system based on short, low duty cyclepulses. In the widest bandwidth embodiment, the resulting waveformapproaches one cycle per pulse at the center frequency. In more narrowband embodiments, each pulse consists of a burst of cycles usually withsome spectral shaping to control the bandwidth to meet desiredproperties such as out of band emissions or in-band spectral flatness,or time domain peak power or burst off time attenuation.

For system analysis purposes, it is convenient to model the desiredwaveform in an ideal sense to provide insight into the optimum behaviorfor detail design guidance. One such waveform model that has been usefulis the Gaussian monocycle as shown in FIG. 1A. This waveform isrepresentative of the transmitted pulse produced by a step function intoan ultra-wideband antenna. The basic equation normalized to a peak valueof 1 is as follows:

${f_{mono}(t)} = {\sqrt{e}\left( \frac{t}{\sigma} \right)e^{\frac{- t^{2}}{2\sigma^{2}}}}$Where,

-   -   σ is a time scaling parameter,    -   t is time,    -   f_(mono)(t) is the waveform voltage, and    -   e is the natural logarithm base.

The frequency domain spectrum of the above waveform is shown in FIG. 1B.The corresponding equation is:F _(mono)(f)=(2π)3/2σfe ^(−2(πof)) ²

The center frequency (f_(c)), or frequency of peak spectral density is:

$f_{c} = \frac{1}{2{\pi\sigma}}$

These pulses, or bursts of cycles, may be produced by methods describedin the patents referenced above or by other methods that are known toone of ordinary skill in the art. Any practical implementation willdeviate from the ideal mathematical model by some amount. In fact, thisdeviation from ideal may be substantial and yet yield a system withacceptable performance. This is especially true for microwaveimplementations, where precise waveform shaping is difficult to achieve.These mathematical models are provided as an aid to describing idealoperation and are not intended to limit the invention. In fact, anyburst of cycles that adequately fills a given bandwidth and has anadequate on-off attenuation ratio for a given application will serve thepurpose of this invention.

A Pulse Train

Impulse radio systems can deliver one or more data bits per pulse;however, impulse radio systems more typically use pulse trains, notsingle pulses, for each data bit. As described in detail in thefollowing example system, the impulse radio transmitter produces andoutputs a train of pulses for each bit of information.

Prototypes built by the inventors have pulse repetition frequenciesincluding 0.7 and 10 megapulses per second (Mpps, where each megapulseis 10⁶ pulses). FIGS. 2A and 2B are illustrations of the output of atypical 10 Mpps system with uncoded, unmodulated, 0.5 nanosecond (ns)pulses 102. FIG. 2A shows a time domain representation of this sequenceof pulses 102. FIG. 2B, which shows 60 MHZ at the center of the spectrumfor the waveform of FIG. 2A, illustrates that the result of the pulsetrain in the frequency domain is to produce a spectrum comprising a setof lines 204 spaced at the frequency of the 10 Mpps pulse repetitionrate. When the full spectrum is shown, the envelope of the line spectrumfollows the curve of the single pulse spectrum 104 of FIG. 1B. For thissimple uncoded case, the power of the pulse train is spread amongroughly two hundred comb lines. Each comb line thus has a small fractionof the total power and presents much less of an interference problem toreceiver sharing the band.

It can also be observed from FIG. 2A that impulse radio systemstypically have very low average duty cycles resulting in average powersignificantly lower than peak power. The duty cycle of the signal in thepresent example is 0.5%, based on a 0.5 ns pulse in a 100 ns interval.

Coding for Energy Smoothing and Channelization

For high pulse rate systems, it may be necessary to more finely spreadthe spectrum than is achieved by producing comb lines. This may be doneby pseudo-randomly positioning each pulse relative to its nominalposition.

FIG. 3 is a plot illustrating the impact of a pseudo-noise (PN) codedither on energy distribution in the frequency domain (A pseudo-noise,or PN code is a set of time positions defining the pseudo-randompositioning for each pulse in a sequence of pulses). FIG. 3, whencompared to FIG. 2B, shows that the impact of using a PN code is todestroy the comb line structure and spread the energy more uniformly.This structure typically has slight variations which are characteristicof the specific code used.

The PN code also provides a method of establishing independentcommunication channels using impulse radio. PN codes can be designed tohave low cross correlation such that a pulse train using one code willseldom collide on more than one or two pulse positions with a pulsestrain using another code during any one data bit time. Since a data bitmay comprise hundreds of pulses, this represents a substantialattenuation of the unwanted channel.

Modulation

Any aspect of the waveform can be modulated to convey information.Amplitude modulation, phase modulation, frequency modulation, time shiftmodulation and M-ary versions of these have been proposed. Both analogand digital forms have been implemented. Of these, digital time shiftmodulation has been demonstrated to have various advantages and can beeasily implemented using a correlation receiver architecture.

Digital time shift modulation can be implemented by shifting the codedtime position by an additional amount (that is, in addition to PN codedither) in response to the information signal. This amount is typicallyvery small relative to the PN code shift. In a 10 Mpps system with acenter frequency of 2 GHz., for example, the PN code may command pulseposition variations over a range of 100 ns; whereas, the informationmodulation may only deviate the pulse position by 150 ps.

Thus, in a pulse train of n pulses, each pulse is delayed a differentamount from its respective time base clock position by an individualcode delay amount plus a modulation amount, where n is the number ofpulses associated with a given data symbol digital bit.

Modulation further smooths the spectrum, minimizing structure in theresulting spectrum.

Reception and Demodulation

Clearly, if there were a large number of impulse radio users within aconfined area, there might be mutual interference. Further, while the PNcoding minimizes that interference, as the number of users rises, theprobability of an individual pulse from one user's sequence beingreceived simultaneously with a pulse from another user's sequenceincreases. Impulse radios are able to perform in these environments, inpart, because they do not depend on receiving every pulse. The impulseradio receiver performs a correlating, synchronous receiving function(at the RF level) that uses a statistical sampling and combining of manypulses to recover the transmitted information.

Impulse radio receivers typically integrate from 1 to 1000 or morepulses to yield the demodulated output. The optimal number of pulsesover which the receiver integrates is dependent on a number ofvariables, including pulse rate, bit rate, interference levels, andrange.

Interference Resistance

Besides channelization and energy smoothing, the PN coding also makesimpulse radios highly resistant to interference from all radiocommunications systems, including other impulse radio transmitters. Thisis critical as any other signals within the band occupied by an impulsesignal potentially interfere with the impulse radio. Since there arecurrently no unallocated bands available for impulse systems, they mustshare spectrum with other conventional radio systems without beingadversely affected. The PN code helps impulse systems discriminatebetween the intended impulse transmission and interfering transmissionsfrom others.

FIG. 4 illustrates the result of a narrow band sinusoidal interferencesignal 402 overlaying an impulse radio signal 404. At the impulse radioreceiver, the input to the cross correlation would include the narrowband signal 402, as well as the received ultrawide-band impulse radiosignal 404. The input is sampled by the cross correlator with a PNdithered template signal 406. Without PN coding, the cross correlationwould sample the interfering signal 402 with such regularity that theinterfering signals could cause significant interference to the impulseradio receiver. However, when the transmitted impulse signal is encodedwith the PN code dither (and the impulse radio receiver template signal406 is synchronized with that identical PN code dither) the correlationsamples the interfering signals pseudo-randomly. The samples from theinterfering signal add incoherently, increasing roughly according tosquare root of the number of samples integrated; whereas, the impulseradio samples add coherently, increasing directly according to thenumber of samples integrated. Thus, integrating over many pulsesovercomes the impact of interference.

Processing Gain

Impulse radio is resistant to interference because of its largeprocessing gain. For typical spread spectrum systems, the definition ofprocessing gain, which quantifies the decrease in channel interferencewhen wide-band communications are used, is the ratio of the bandwidth ofthe channel to the bit rate of the information signal. For example, adirect sequence spread spectrum system with a 10 kHz informationbandwidth and a 10 MHZ channel bandwidth yields a processing gain of1000 or 30 dB. However, far greater processing gains are achieved withimpulse radio systems, where for the same 10 KHz information bandwidthis spread across a much greater 2 GHz. channel bandwidth, thetheoretical processing gain is 200,000 or 53 dB.

Capacity

It has been shown theoretically, using signal to noise arguments, thatthousands of simultaneous voice channels are available to an impulseradio system as a result of the exceptional processing gain, which isdue to the exceptionally wide spreading bandwidth.

For a simplistic user distribution, with N interfering users of equalpower equidistant from the receiver, the total interference signal tonoise ratio as a result of these other users can be described by thefollowing equation:

$V_{tot}^{2} = \frac{N\;\sigma^{2}}{\sqrt{Z}}$

-   -   Where V² _(tot) is the total interference signal to noise ratio        variance, at the receiver;    -   N is the number of interfering users;    -   σ² is the signal to noise ratio variance resulting from one of        the interfering signals with a single pulse cross correlation;        and    -   Z is the number of pulses over which the receiver integrates to        recover the modulation.

This relationship suggests that link quality degrades gradually as thenumber of simultaneous users increases. It also shows the advantage ofintegration gain. The number of users that can be supported at the sameinterference level increases by the square root of the number of pulsesintegrated.

Multipath and Propagation

One of the striking advantages of impulse radio is its resistance tomultipath fading effects. Conventional narrow band systems are subjectto multipath through the Rayleigh fading process, where the signals frommany delayed reflections combine at the receiver antenna according totheir seemingly random relative phases. This results in possiblesummation or possible cancellation, depending on the specificpropagation to a given location. This situation occurs where the directpath signal is weak relative to the multipath signals, which representsa major portion of the potential coverage of a radio system. In mobilesystems, this results in wild signal strength fluctuations as a functionof distance traveled, where the changing mix of multipath signalsresults in signal strength fluctuations for every few feet of travel.

Impulse radios, however, can be substantially resistant to theseeffects. Impulses arriving from delayed multipath reflections typicallyarrive outside of the correlation time and thus can be ignored. Thisprocess is described in detail with reference to FIGS. 5A and 5B. InFIG. 5A, three propagation paths are shown. The direct path representingthe straight line distance between the transmitter and receiver is theshortest. Path 1 represents a grazing multipath reflection, which isvery close to the direct path. Path 2 represents a distant multipathreflection. Also shown are elliptical (or, in space, ellipsoidal) tracesthat represent other possible locations for reflections with the sametime delay.

FIG. 5B represents a time domain plot of the received waveform from thismultipath propagation configuration. This figure comprises three doubletpulses as shown in FIG. 1A. The direct path signal is the referencesignal and represents the shortest propagation time. The path 1 signalis delayed slightly and actually overlaps and enhances the signalstrength at this delay value. Note that the reflected waves are reversedin polarity. The path 2 signal is delayed sufficiently that the waveformis completely separated from the direct path signal. If the correlatortemplate signal is positioned at the direct path signal, the path 2signal will produce no response. It can be seen that only the multipathsignals resulting from very close reflectors have any effect on thereception of the direct path signal. The multipath signals delayed lessthan one quarter wave (one quarter wave is about 1.5 inches, or 3.5 cmat 2 GHz center frequency) are the only multipath signals that canattenuate the direct path signal. This region is equivalent to the firstFresnel zone familiar to narrow band systems designers. Impulse radio,however, has no further nulls in the higher Fresnel zones. The abilityto avoid the highly variable attenuation from multipath gives impulseradio significant performance advantages.

FIG. 5A illustrates a typical multipath situation, such as in abuilding, where there are many reflectors 5A04, 5A05 and multiplepropagation paths 5A02, 5A01. In this figure, a transmitter TX 5A06transmits a signal which propagates along the multiple propagation paths5A02, 5A04 to receiver RX 5A08, where the multiple reflected signals arecombined at the antenna.

FIG. 5B illustrates a resulting typical received composite pulsewaveform resulting from the multiple reflections and multiplepropagation paths 5A01, 5A02. In this figure, the direct path signal5A01 is shown as the first pulse signal received. The multiple reflectedsignals (“multipath signals”, or “multipath”) comprise the remainingresponse as illustrated.

FIGS. 5C, 5D, and 5E represent the received signal from a TM-UWBtransmitter in three different multipath environments. These figures arenot actual signal plots, but are hand drawn plots approximating typicalsignal plots. FIG. 5C illustrates the received signal in a very lowmultipath environment. This may occur in a building where the receiverantenna is in the middle of a room and is one meter from thetransmitter. This may also represent signals received from somedistance, such as 100 meters, in an open field where there are noobjects to produce reflections. In this situation, the predominant pulseis the first received pulse and the multipath reflections are too weakto be significant. FIG. 5D illustrates an intermediate multipathenvironment. This approximates the response from one room to the next ina building. The amplitude of the direct path signal is less than in FIG.5C and several reflected signals are of significant amplitude. (Notethat the scale has been increased to normalize the plot.) FIG. 5Eapproximates the response in a severe multipath environment such as:propagation through many rooms; from corner to corner in a building;within a metal cargo hold of a ship; within a metal truck trailer; orwithin an intermodal shipping container. In this scenario, the main pathsignal is weaker than in FIG. 5D. (Note that the scale has beenincreased again to normalize the plot.) In this situation, the directpath signal power is small relative to the total signal power from thereflections.

An impulse radio receiver in accordance with the present invention canreceive the signal and demodulate the information using either thedirect path signal or any multipath signal peak having sufficient signalto noise ratio. Thus, the impulse radio receiver can select thestrongest response from among the many arriving signals. In order forthe signals to cancel and produce a null at a given location, dozens ofreflections would have to be cancelled simultaneously and preciselywhile blocking the direct path—a highly unlikely scenario. This timeseparation of mulitipath signals together with time resolution andselection by the receiver permit a type of time diversity that virtuallyeliminates cancellation of the signal. In a multiple correlator rakereceiver, performance is further improved by collecting the signal powerfrom multiple signal peaks for additional signal to noise performance.

Where the system of FIG. 5A is a narrow band system and the delays aresmall relative to the data bit time, the received signal is a sum of alarge number of sine waves of random amplitude and phase. In theidealized limit, the resulting envelope amplitude has been shown tofollow a Rayleigh probability distribution as follows:

${p(r)} = {\frac{1}{\sigma^{2}}{\exp\left( \frac{- r^{2}}{2\sigma^{2}} \right)}}$

where r is the envelope amplitude of the combined multipath signals, and2σ² is the RMS power of the combined mulitpath signals.

This distribution shown in FIG. 5F. It can be seen in FIG. 5F that 10%of the time, the signal is more than 16 dB attenuated. This suggeststhat 16 dB fade margin is needed to provide 90% link availability.Values of fade margin from 10 to 40 dB have been suggested for variousnarrow band systems, depending on the required reliability. Thischaracteristic has been the subject of much research and can bepartially improved by such techniques as antenna and frequencydiversity, but these techniques result in additional complexity andcost.

In a high multipath environment such as inside homes, offices,warehouses, automobiles, trailers, shipping containers, or outside inthe urban canyon or other situations where the propagation is such thatthe received signal is primarily scattered energy, impulse radio,according to the present invention, can avoid the Rayleigh fadingmechanism that limits performance of narrow band systems. This isillustrated in FIGS. 5G and 5H in a transmit and receive system in ahigh multipath environment 5G00, wherein the transmitter 5G06 transmitsto receiver 5G08 with the signals reflecting off reflectors 5G03 whichform multipaths 5G02. The direct path is illustrated as 5G01 with thesignal graphically illustrated at 5H02, with the vertical axis being thesignal strength in volts and horizontal axis representing time innanoseconds. Multipath signals are graphically illustrated at 5H04.

Distance Measurement

Important for positioning, impulse systems can measure distances toextremely fine resolution because of the absence of ambiguous cycles inthe waveform. Narrow band systems, on the other hand, are limited to themodulation envelope and cannot easily distinguish precisely which RFcycle is associated with each data bit because the cycle-to-cycleamplitude differences are so small they are masked by link or systemnoise. Since the impulse radio waveform has no multi-cycle ambiguity,this allows positive determination of the waveform position to less thana wavelength-potentially, down to the noise floor of the system. Thistime position measurement can be used to measure propagation delay todetermine link distance, and once link distance is known, to transfer atime reference to an equivalently high degree of precision. Theinventors of the present invention have built systems that have shownthe potential for centimeter distance resolution, which is equivalent toabout 30 ps of time transfer resolution. See, for example, commonlyowned, co-pending application Ser. No. 09/045,929, filed Mar. 23, 1998,titled “Ultrawide-Band Position Determination System and Method”, nowU.S. Pat. No. 6,133,876, issued Oct. 17, 2000, and 09/083,993, filed May26, 1998, titled “System and Method for Distance Measurement by Inphaseand Quadrature Signals in a Radio System”, now U.S. Pat. No. 6,111,536,issued Aug. 29, 2000, both of which are incorporated herein byreference.

In addition to the methods articulated above, impulse radio technologyalong with Time Division Multiple Access algorithms and Time Domainpacket radios can achieve geo-positioning capabilities in a radionetwork. This geo-positioning method allows ranging to occur within anetwork of radios without the necessity of a full duplex exchange amongevery pair of radios.

FIG. 9A illustrates an example of a four slot TDMA network 90A. We beginwith all radios off the air. As the first radio, 92A, comes on, itpauses to listen to the current network traffic. After a reasonabledelay, it powers on and, having heard no other traffic, takes control ofthe first slot shown in FIG. 9B as 92B. While online, it willperiodically send a hello request containing identifying informationshowing it owns slot 1. Although the network is considered adhoc, theradio that owns the first TDMA slot has some unique responsibilities.

Radio B, 94A, powers up next and begins to listen to network traffic. Itnotes that Radio A, 92A, is on the air in the first slot. Radio B, 94A,acquires slot 2; 94B, and transmits a hello request at the slot twoposition 2, 94B. The hello request prompts an exchange with Radio A,92A, as soon as his slot comes available. Radio A transmits a packetthat will result in the acquisition of two pieces of information. RadioA, 92A, sends a SYNC packet containing a request for an immediateacknowledgement. Radio B, 94A, is thereby given permission to respondduring Radio A's slot time. Radio B, 94A, transmits a SYNC ACK packet inreturn. Radio A, 92A, then calculates the distance to Radio B, 94A, andproperly adjusts the synchronization clock for the distance and sendsthe current time, adjusted for distance, to Radio B, 94A. At this pointRadio A's, 92A, clock is synchronized with Radio B, 94A. Once thisoccurs, any time Radio A, 92A, transmits, Radio B, 94A, is capable ofcalculating the distance to Radio A, 92A, without a full duplexexchange. Also any time Radio B, 94A, transmits, Radio A, 94A, iscapable of calculating the distance to Radio B, 94A.

Through periodic SYNC packets to radio C, 98A, and radio D, 96A, on thenetwork, clock synchronization could be maintained throughout the entirenetwork of radios. Assuming that radio A, 92A, radio B, 94A, radio C,98A and radio D, 96A, always transmit packets at the immediate start oftheir slot times 92B, 94B, 96B, and 98B, this system would allow allradios on a network to immediately calculate the distance to any otherradio on the network whenever a radio transmitted a packet.

Exemplary Transceiver Implementation

Transmitter

An exemplary embodiment of an impulse radio transmitter 602 of animpulse radio communication system having one subcarrier channel willnow be described with reference to FIG. 6.

The transmitter 602 comprises a time base 604 that generates a periodictiming signal 606. The time base 604 typically comprises a voltagecontrolled oscillator (VCO), or the like, having a high timing accuracyand low jitter, on the order of picoseconds (ps). The voltage control toadjust the VCO center frequency is set at calibration to the desiredcenter frequency used to define the transmitter's nominal pulserepetition rate. The periodic timing signal 606 is supplied to aprecision timing generator 608.

The precision timing generator 608 supplies synchronizing signals 610 tothe code source 612 and utilizes the code source output 614 togetherwith an internally generated subcarrier signal (which is optional) andan information signal 616 to generate a modulated, coded timing signal618. The code source 612 comprises a storage device such as a randomaccess memory (RAM), read only memory (ROM), or the like, for storingsuitable PN codes and for outputting the PN codes as a code signal 614.Alternatively, maximum length shift registers or other computationalmeans can be used to generate the PN codes.

An information source 620 supplies the information signal 616 to theprecision timing generator 608. The information signal 616 can be anytype of intelligence, including digital bits representing voice, data,imagery, or the like, analog signals, or complex signals.

A pulse generator 622 uses the modulated, coded timing signal 618 as atrigger to generate output pulses. The output pulses are sent to atransmit antenna 624 via a transmission line 626 coupled thereto. Theoutput pulses are converted into propagating electromagnetic pulses bythe transmit antenna 624. In the present embodiment, the electromagneticpulses are called the emitted signal, and propagate to an impulse radioreceiver 702, such as shown in FIG. 7, through a propagation medium,such as air, in a radio frequency embodiment. In a preferred embodiment,the emitted signal is wide-band or ultrawide-band, approaching amonocycle pulse as in FIG. 1A. However, the emitted signal can bespectrally modified by filtering of the pulses. This bandpass filteringwill cause each monocycle pulse to have more zero crossings (morecycles) in the time domain. In this case, the impulse radio receiver canuse a similar waveform as the template signal in the cross correlatorfor efficient conversion.

Receiver

An exemplary embodiment of an impulse radio receiver (hereinafter calledthe receiver) for the impulse radio communication system is nowdescribed with reference to FIG. 7.

The receiver 702 comprises a receive antenna 704 for receiving apropagated impulse radio signal 706. A received signal 708 is input to across correlator or sampler 710 via a receiver transmission line,coupled to the receive antenna 704, and producing a baseband output 712.

The receiver 702 also includes a precision timing generator 714, whichreceives a periodic timing signal 716 from a receiver time base 718.This time base 718 is adjustable and controllable in time, frequency, orphase, as required by the lock loop in order to lock on the receivedsignal 708. The precision timing generator 714 provides synchronizingsignals 720 to the code source 722 and receives a code control signal724 from the code source 722. The precision timing generator 714utilizes the periodic timing signal 716 and code control signal 724 toproduce a coded timing signal 726. The template generator 728 istriggered by this coded timing signal 726 and produces a train oftemplate signal pulses 730 ideally having waveforms substantiallyequivalent to each pulse of the received signal 708. The code forreceiving a given signal is the same code utilized by the originatingtransmitter to generate the propagated signal. Thus, the timing of thetemplate pulse train matches the timing of the received signal pulsetrain, allowing the received signal 708 to be synchronously sampled inthe correlator 710. The correlator 710 ideally comprises a multiplierfollowed by a short term integrator to sum the multiplier product overthe pulse interval.

The output of the correlator 710 is coupled to a subcarrier demodulator732, which demodulates the subcarrier information signal from thesubcarrier. The purpose of the optional subcarrier process, when used,is to move the information signal away from DC (zero frequency) toimprove immunity to low frequency noise and offsets. The output of thesubcarrier demodulator is then filtered or integrated in the pulsesummation stage 734. A digital system embodiment is shown in FIG. 7. Inthis digital system, a sample and hold 736 samples the output 735 of thepulse summation stage 734 synchronously with the completion of thesummation of a digital bit or symbol. The output of sample and hold 736is then compared with a nominal zero (or reference) signal output in adetector stage 738 to determine an output signal 739 representing thedigital state of the output voltage of sample and hold 736.

The baseband signal 712 is also input to a lowpass filter 742 (alsoreferred to as lock loop filter 742). A control loop comprising thelowpass filter 742, time base 718, precision timing generator 714,template generator 728, and correlator 710 is used to generate an errorsignal 744. The error signal 744 provides adjustments to the adjustabletime base 718 to time position the periodic timing signal 726 inrelation to the position of the received signal 708.

In a transceiver embodiment, substantial economy can be achieved bysharing part or all of several of the functions of the transmitter 602and receiver 702. Some of these include the time base 718, precisiontiming generator 714, code source 722, antenna 704, and the like.

FIGS. 8-10 illustrate the cross correlation process and the correlationfunction. FIG. 8 shows the waveform of a template signal. FIG. 8B showsthe waveform of a received impulse radio signal at a set of severalpossible time offsets. FIG. 9 represents the output of the correlator(multiplier and short time integrator) for each of the time offsets ofFIG. 8B. Thus, this graph does not show a waveform that is a function oftime, but rather a function of time-offset. For any given pulsereceived, there is only one corresponding point which is applicable onthis graph. This is the point corresponding to the time offset of thetemplate signal used to receive that pulse. Further examples and detailsof precision timing can be found described in U.S. Pat. No. 5,677,927,and commonly owned co-pending application Ser. No. 09/146,524, filedSep. 3, 1998, titled “Precision Timing Generator System and Method”, nowU.S. Pat. No. 6,304,623, issued Oct. 16, 2001, both of which areincorporated herein by reference.

Impulse Radio as Used in the Present Invention

Utilizing the unique properties of impulse radio, the current state ofthe art in positioning systems is dramatically improved. By using thepositioning techniques in the prior impulse radio positioning patentswhich have been incorporated by reference, as well as the aforementionednovel positioning TDMA technique, in the following architectures, novelimpulse radio positioning systems and methods are herein enabled.

Synchronized Transceiver Tracking

FIG. 10 illustrates a Synchronized Transceiver Tracking, wherein anetwork of fixed-location reference transceivers (two-way impulseradios) allow the position of multiple mobile transceivers (two-wayimpulse radios) to be determined. This architecture is perhaps the mostgeneric of the impulse radio geo-positioning architectures since boththe mobile and reference radios are full two-way transceivers. Thenetwork is designed to be scalable, allowing from very few reference andmobile radios to a very large number.

FIG. 10 is a block diagram showing a simple implementation of thisarchitecture. This particular example shows a system of four referenceradios (R1, 1002, through R4, 1008) and two mobile radios (M1, 1012, andM2, 1010). The arrows between the radios represent two-way data and/orvoice links. A fully inter-connected network would have every radiocontinually communicating with every other radio, but this is notrequired and can be dependent upon the needs of the particularapplication.

Each radio is a two-way transceiver; thus each link between radios istwo-way (duplex). Precise ranging information (the distance between tworadios) is distributed around the network in such a way as to allow themobile radios (M1, 1012, and M2, 1010, in FIG. 10) to determine theirprecise three-dimensional position within a local coordinate system.This position, along with other data or voice traffic, can then berelayed from the mobile radios back to the reference master radio (R1,1002), one of the other reference relay radios (R2, 1004, through R4,1008 in FIG. 10), or to other mobile radios such as M2, 1010, in FIG.10).

The radios used in this architecture are impulse radio two-waytransceivers. The reference and mobile radio hardware is essentially thesame. The firmware, however, varies slightly based on the functions eachradio must perform. For example, R1, 1002, can designate as thereference master radio. As the master, it directs the passing ofinformation and typically will be responsible for collecting all thedata for external graphical display. The remaining reference relayradios contain a separate version of the firmware, the primarydifference being the different parameters or information that eachreference relay radio must provide the network. Finally, the mobileradios have their own firmware version that calculates their positionand displays it locally if desired.

In FIG. 10, each radio link is a two-way link that allows for thepassing of information, both data and/or voice. The data-rates betweeneach radio link is a function of several variables including the numberof pulses integrated to get a single bit, the number of bits per dataparameter, the length of any headers required in the messages, the rangebin size, and the number of radios in the network.

By transmitting in assigned time slots and by carefully listening to theother radios transmit in their assigned transmit time slots, the entiregroup of radios within the network, both mobile and reference, will beable to synchronize themselves. The oscillators used on the impulseradio boards will drift slowly in time, thus requiring continualmonitoring and adjustment of synchronization. The accuracy of thissynchronization process (timing) is dependent upon several factors.These factors include how often and how long each radio transmits.

The purpose of the impulse radio geo-positioning network is to be ableto track mobile radios. Tracking is accomplished by stepping throughseveral well-defined steps. The first step is for the reference radiosto synchronize together and begin passing information. Then, when amobile radio enters the network area, it synchronizes itself to thepreviously synchronized reference radios. Once the mobile radio issynchronized, it begins collecting and time-tagging range measurementsfrom any available reference (or other mobile) radio. The mobile radiothen takes these time-tagged ranges and, using a least squares-based orsimilar estimator, calculates the mobile radio position in localcoordinates. If the situation warrants and the conversion possible, thelocal coordinates can be converted to any one of the worldwidecoordinates such as Earth Centered Inertial (ECI), Earth Centered EarthFixed (ECEF), or J2000 (inertial coordinates fixed to year 2000).Finally, the mobile radio forwards its position solution to thereference master radio for storage and real-time display.

Unsynchronized Transceiver Tracking

FIG. 11 illustrates Unsynchronized Transceiver Tracking, which is anetwork of fixed-location, unsynchronized reference impulse radiotransceivers, 1102-1108, which allows the position of multiple mobileimpulse radio transceivers, 1110 and 1112, to be determined. Thisarchitecture is similar to Synchronized Transceiver Tracking of FIG. 10,except that the reference receivers are not time-synchronized. Both themobile and reference radios for this architecture are full two-waytransceivers. The network is designed to be scalable, allowing from veryfew reference and mobile radios to a very large number of both.

This particular embodiment of FIG. 11 shows a system of four referenceradios (R1, 1102 through R4, 1108) and two mobile radios (M1, 1110 andM2, 1112). The arrows between the radios represent two-way data and/orvoice links. A fully inter-connected network would have every radiocontinually communicating with every other radio, but this is notrequired and can be defined as to the needs of the particularapplication. Each radio is a two-way transceiver; thus each link betweenradios is two-way (duplex). Precise ranging information (the distancebetween two radios) is distributed around the network in such a way asto allow the mobile radios (M1, 1110 and M2, 1112 in FIG. 11) todetermine their precise three-dimensional position within a localcoordinate system. This position, along with other data or voicetraffic, can then be relayed from the mobile radios back to thereference master radio (R1, 1102), one of the other reference relayradios (R2, 1104 through RN), or to other mobile radios.

The radios used in the architecture of FIG. 11 are impulse radio two-waytransceivers. The reference and mobile radio hardware is essentially thesame. The firmware, however, varies slightly based on the functions eachradio must perform. For example, R1, 1102, is designated as thereference master radio. It directs the passing of information, andtypically will be responsible for collecting all the data for externalgraphical display. The remaining reference relay radios contain aseparate version of the firmware, the primary difference being thedifferent parameters or information that each reference relay radio mustprovide the network. Finally, the mobile radios have their own firmwareversion that calculates their position and displays it locally, ifdesired.

Each radio link is a two-way link that allows for the passing ofinformation, data and/or voice. The data-rates between each radio linkis a function of several variables including the number of pulsesintegrated to get a single bit, the number of bits per data parameter,the length of any headers required in the messages, the range bin size,and the number of radios in the network.

Unlike the radios in the Synchronized Transceiver Tracking architecture,the reference radios in this architecture are not time-synchronized as anetwork. These radios simply operate independently (free-running),providing ranges to the mobile radios either periodically, randomly, orwhen tasked. Depending upon the application and situation, the referenceradios may or may not talk to other reference radios in the network.

As with the architecture of FIG. 10, the purpose of the impulse radiogeo-positioning network is to be able to track mobile radios. Trackingis accomplished by stepping through several steps. These steps aredependent upon the way in which the reference radios range with themobile radios (periodically, randomly, or when tasked). When a mobileradio enters the network area, it either listens for reference radios tobroadcasts, then responds, or it queries (tasks) the desired referenceradios to respond. The mobile radio begins collecting and time-taggingrange measurements from reference (or other mobile) radios. The mobileradio then takes these time-tagged ranges and, using a leastsquares-based or similar estimator, calculates the mobile radio positionin local coordinates. If the situation warrants and the conversionpossible, the local coordinates can be converted to any one of theworldwide coordinates such as Earth Centered Inertial (ECI), EarthCentered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed toyear 2000). Finally, the mobile radio forwards its position solution tothe reference master radio for storage and real-time display if desired,1114.

Synchronized Transmitter Tracking

In Synchronized Transmitter Tracking, a network of fixed-location twoway reference impulse radio transceivers allow the position of multiplemobile impulse radio transmitters to be determined. This architecture isperhaps the simplest of the impulse radio geo-positioning architectures,from the point-of-view of the mobile radio, since the mobile radiossimply transmits in a free-running sense. The network is designed to bescalable, allowing from very few reference and mobile radios to a verylarge number. This architecture is especially applicable to an “RF tag”(radio frequency tag) type of application.

FIG. 12 is a block diagram showing a simple implementation of thisarchitecture. This particular example shows a system of four referenceradios (R1, 1202 through R4, 1208) and two mobile radios (M1, 1210 andM2, 1212). The arrows between the radios represent two-way and one-waydata and/or voice links. Notice that the mobile impulse radios onlytransmit, thus they do not receive the transmissions from the othermobile radios.

Each reference radio is a two-way transceiver; thus each link betweenreference radios is two-way (duplex). Precise ranging information (thedistance between two radios) is distributed around the reference radionetwork in such a way as to allow the synchronized reference radios toreceive the mobile radio transmissions (M1 and M2 in FIG. 1) in order todetermine the mobile radio precise three-dimensional position within alocal coordinate system. This position, along with other data or voicetraffic, can then be relayed from the reference relay radios back to thereference master radio (R1).

The reference radios used in this architecture are impulse radio two-waytransceivers, the mobile impulse radios are one-way transmitters. Thefirmware in the radios varies slightly based on the functions each radiomust perform. For example, R1, 1202, is designated as the referencemaster radio. It directs the passing of information, and typically willbe responsible for collecting all the data for external graphicaldisplay. The remaining reference relay radios contain a separate versionof the firmware, the primary difference being the different parametersor information that each reference relay radio must provide the network.Finally, the mobile radios have their own firmware version thattransmits pulses in predetermined sequences.

Each reference radio link is a two-way link that allows for the passingof information, data and/or voice. The data-rates between each radiolink is a function of several variables including the number of pulsesintegrated to get a single bit, the number of bits per data parameter,the length of any headers required in the messages, the range bin size,and the number of radios in the network.

By transmitting in assigned time slots and by carefully listening to theother radios transmit in their assigned transmit time slots, the entiregroup of reference radios within the network will be able to synchronizethemselves. The oscillators used on the impulse radio boards will driftslowly in time, thus requiring continual monitoring and adjustment ofsynchronization. The accuracy of this synchronization process (timing)is dependent upon several factors. These factors include how often andhow long each radio transmits along with other factors. The mobileradios, since they are transmit-only transmitters, are nottime-synchronized to the synchronized reference radio network.

The purpose of the impulse radio geo-positioning network is to be ableto track mobile radios. Tracking is accomplished by stepping throughseveral well-defined steps. The first step is for the reference radiosto synchronize together and begin passing information. Then, when amobile radio enters the network area and begins to transmit pulses, thereference radios pick up these pulses as time-of-arrivals (TOAs).Multiple TOAs collected by different synchronized reference radios arethen converted to ranges, which are then used to calculate mobile radioXYZ position in local coordinates. If the situation warrants and theconversion possible, the local coordinates can be converted to any oneof the worldwide coordinates such as Earth Centered Inertial (ECI),Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixedto year 2000).

Unsynchronized Transmitter Tracking

In Unsynchronized Transmitter Tracking, a network of fixed-locationimpulse radio reference transceivers allow the position of multiplemobile impulse radio transmitters to be determined. This architecture isvery similar to the Synchronized Transmitter Tracking architectureexcept that the reference radios are not synchronized in time. In otherwords, both the reference radios and the mobile radios are free-running.The network is designed to be scalable, allowing from very few referenceand mobile radios to a very large number. This architecture isespecially applicable to an “RF tag” type of application.

FIG. 13 is a block diagram showing a simple implementation of thisarchitecture. This particular embodiment shows a system of fourreference radios (R1, 1302 through R4, 1308) and two mobile radios (M1,1310 and M2, 1312). The arrows between the radios represent two-way andone-way data and/or voice links. Notice that the mobile radios onlytransmit, thus they do not receive the transmissions from the othermobile radios. Unlike the Synchronous Transmitter Tracking architecture,the reference radios in this architecture are free-running(unsynchronized). There are several ways to implement this design, themost common involves relaying the time-of-arrival (TOA) pulses from themobile and reference radios, as received at the reference radios, backto the reference master radio.

Each reference radio in this architecture is a two-way impulse radiotransceiver; thus each link between reference radios can be eithertwo-way (duplex) or one-way (simplex). TOA information will typically betransmitted from the reference radios back to the reference master radiowhere the TOAs will be converted to ranges and then XYZ position, whichcan then be displayed, 1314.

The reference radios used in this architecture are impulse radio two-waytransceivers, the mobile radios are one-way impulse radio transmitters.The firmware in the radios varies slightly based on the functions eachradio must perform. For example, R1, 1302 is designated as the referencemaster radio. It collects the TOA information, and typically will beresponsible for forwarding tracking data for external graphical display,1314. The remaining reference relay radios contain a separate version ofthe firmware, the primary difference being the different parameters orinformation that each reference relay radio must provide the network.Finally, the mobile radios have their own firmware version thattransmits pulses in predetermined sequences.

Each reference radio link is a two-way link that allows for the passingof information, data and/or voice. The data-rates between each radiolink is a function of several variables including the number of pulsesintegrated to get a single bit, the number of bits per data parameter,the length of any headers required in the messages, the range bin size,and the number of radios in the network.

Since the reference radios and mobile radios are free-running,synchronization is actually done by the reference master impulse radio1302 alone. The oscillators used in the impulse radios will drift slowlyin time, thus likely requiring continual monitoring and adjustment ofsynchronization at the reference master radio. The accuracy of thissynchronization (timing) is dependent upon several factors. Thesefactors include how often and how long each radio transmits along withother factors.

The purpose of the impulse radio geo-positioning network is to be ableto track mobile radios. Tracking is accomplished by stepping throughseveral steps. The most likely method is to have each reference radioperiodically (randomly) transmit a pulse sequence. Then, when a mobileradio enters the network area and begins to transmit pulses, thereference radios pick up these pulses as time-of-arrivals (TOAs) as wellas the pulses (TOAs) transmitted by the other reference radios. TOAs canthen either be relayed back to the reference master radio or justcollected directly (assuming it can pick up all the transmissions). Thereference master radios then converts these TOAs to ranges, which arethen used to calculate mobile radio XYZ position in local coordinates.If the situation warrants and the conversion possible, the localcoordinates can be converted to any one of the worldwide coordinatessuch as Earth Centered Inertial (ECI), Earth Centered Earth Fixed(ECEF), or J2000 (inertial coordinates fixed to year 2000).

Synchronized Receiver Tracking

In Synchronized Receiver Tracking, a network of fixed-location referenceimpulse radio transceivers allow the position of multiple impulse radiomobile receivers to be determined. This architecture is different fromthe Synchronized Transmitter Tracking architecture in that in thisdesign the mobile receivers will determine their positions but will notbe broadcasting it to anyone (since they are receive-only radios). Thenetwork is designed to be scalable, allowing from very few reference andmobile radios to a very large number of both.

FIG. 14 is a block diagram showing a simple implementation of thisarchitecture. This particular example shows a system of four referenceradios (R1, 1402 through R4, 1408) and two mobile radios (M1, 1410 andM2, 1412). The arrows between the radios represent two-way and one-waydata and/or voice links. Notice that the mobile radios only receivetransmissions from other radios, and do not transmit.

Each reference radio is a two-way transceiver, each mobile radio is areceive-only radio. Precise, synchronized pulses are transmitted by thereference network and received by the other reference radios and themobile radios. The mobile radios takes these times-of-arrival (TOA)pulses, converts them to ranges, then determines its XYZ position. Sincethe mobile radios do not transmit, only they themselves will know theirXYZ position.

The reference radios used in this architecture are impulse radio two-waytransceivers, the mobile radios are receive-only radios. The firmwarefor the radios varies slightly based on the functions each radio mustperform. For example, R1, 1402 is designated as the reference masterradio. It directs the synchronization of the reference radio network.The remaining reference relay radios contain a separate version of thefirmware, the primary difference being the different parameters orinformation that each reference relay radio must provide the network.Finally, the mobile radios have their own firmware version thatcalculates their position and displays it locally if desired.

Each reference radio link is a two-way link that allows for the passingof information, data and/or voice. The mobile radios are receive-only.The data-rates between each radio link is a function of severalvariables including the number of pulses integrated to get a single bit,the number of bits per data parameter, the length of any headersrequired in the messages, the range bin size, and the number of radiosin the network.

By transmitting in assigned time slots and by carefully listening to theother reference radios transmit in their assigned transmit time slots,the entire group of reference radios within the network will be able tosynchronize themselves. The oscillators used on the impulse radio boardswill drift slowly in time, thus requiring continual monitoring andadjustment of synchronization. The accuracy of this synchronization(timing) is dependent upon several factors. These factors include howoften and how long each radio transmits along with other factors.

The purpose of the impulse radio geo-positioning network is to be ableto track mobile radios. Tracking is accomplished by stepping throughseveral well-defined steps. The first step is for the reference radiosto synchronize together and begin passing information. Then, when amobile radio enters the network area, it begins receiving thetime-of-arrival (TOA) pulses from the reference radio network. These TOApulses are converted to ranges, then the ranges are used to determinemobile radio XYZ position in local coordinates using a leastsquares-based estimator. If the situation warrants and the conversionpossible, the local coordinates can be converted to any one of theworldwide coordinates such as Earth Centered Inertial (ECI), EarthCentered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed toyear 2000). Finally, the mobile radio forwards its position solution tothe reference master radio for storage and real-time display.

Unsynchronized Receiver Tracking

In Unsynchronized Receiver Tracking, a network of fixed-locationreference impulse radio transceivers allow the position of multipleimpulse radio mobile receivers to be determined. This architecture isdifferent from the Synchronized Receiver Tracking architecture in thatin this design the reference radios are not time-synchronized. Similarto the Synchronized Receiver Tracking architecture, mobile receive-onlyradios will determine their positions but will not be broadcasting it toanyone (since they are receive-only radios). The network is designed tobe scalable, allowing from very few reference and mobile radios to avery large number of both.

FIG. 15 is a block diagram showing a simple implementation of thisarchitecture. This particular example shows a system of four referenceradios (R1, 1502 through R4, 1508) and two mobile radios (M1, 1510 andM2, 1512). The arrows between the radios represent two-way and one-waydata and/or voice links. Notice that the mobile radios only receivetransmissions from other radios, and do not transmit.

Each reference radio is an impulse radio two-way transceiver, eachmobile radio is a receive-only impulse radio. Precise, unsynchronizedpulses are transmitted by the reference network and received by theother reference impulse radios and the mobile impulse radios. The mobileradios takes these times-of-arrival (TOA) pulses, converts them toranges, then determines its XYZ position. Since the mobile impulseradios do not transmit, only they themselves will know their XYZposition.

The impulse radio reference radios used in this architecture are impulseradio two-way transceivers, the mobile radios are receive-only radios.The firmware for the radios varies slightly based on the functions eachradio must perform. For this design, the reference master radio may beused to provide some synchronization information to the mobile radios orthe mobile radio itself (knowing the XYZ for each reference radio) maydo all of the synchronization internally.

The data-rates between each radio link is a function of severalvariables including the number of pulses integrated to get a single bit,the number of bits per data parameter, the length of any headersrequired in the messages, the range bin size, and the number of impulseradios in the network.

For this architecture, the reference radios transmit in a free-running(unsynchronized) manner. The oscillators used on the impulse radioboards will drift slowly in time, thus requiring continual monitoringand adjustment of synchronization by the reference master radios or themobile radio (whomever is doing the synchronization). The accuracy ofthis synchronization (timing) is dependent upon several factors. Thesefactors include how often and how long each radio transmits along withother factors.

The purpose of the impulse radio geo-positioning network is to be ableto track mobile radios. Tracking is accomplished by stepping throughseveral steps. The first step is for the reference radios to begintransmitting pulses in a free-running (random) manner. Then, when amobile radio enters the network area, it begins receiving thetime-of-arrival (TOA) pulses from the reference radio network. These TOApulses are converted to ranges, then the ranges are used to determinemobile radio XYZ position in local coordinates using a leastsquares-based estimator. If the situation warrants and the conversionpossible, the local coordinates can be converted to any one of theworldwide coordinates such as Earth Centered Inertial (ECI), EarthCentered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed toyear 2000). Finally, the mobile radio forwards its position solution tothe reference master radio for storage and real-time display 1514.

For ease of reference, in the following diagrams the below legendapplies.

Symbols and Definitions

Receiver Radio (receive only) X Transmitter Radio (transmit only)

Transceiver Radio (receive and transmit) R_(i) Reference Radio (fixedlocation) M_(i) Mobile Radio (radio being tracked)

Duplex Radio Link

Simplex Radio Link TOA, DTOA Time of Arrival, Differenced TOA

FIG. 16 shows a Mixed Mode Reference Radio architecture. Thisarchitecture defines a reference network comprised of any combination oftransceivers (R₁, R₂, R₄, R₅), transmitters (R₃), and receivers (R₆).Mobile radios entering this mixed-mode reference network will then usewhatever reference radios are appropriate.

FIG. 17 describes a mixed mode architecture with a combination oftransceivers, transmitters and receivers. Herein, the mobile impulseradios 1712, 1710, 1714 are the mixed mode and the reference impulseradios 1702, 1704, 1706 and 1708 are likely time-synched. In thisillustrative example, the mobile radio 1712 is a transmitter only, 1714is a receiver only and 1710 is a transceiver. The determination of themix of mobile impulse radios and reference radios will be determined bysystem requirements. For example, in the Disney World example the Parkmay want to rent out one device to customers that can locate a child iflost, another to help the customer find bathrooms and roller coasters orboth; and the reference radios must work with both types of mobileimpulse radio systems.

As detailed above and in the referenced patent applications, a steerablenull antennae can be used with impulse radio distance calculations. Byusing the example architecture of FIG. 18, a system can be implementedto take advantage of this distance measuring using steerable nullantennae. Herein, all of the reference radios 1802, 1804, 1806 and 1808or some of them can utilize steerable null antenna designs to direct theimpulse propagation; with one important advantage being the possibilityof using fewer impulse radios or improving range and power requirements.The mobile impulse radio transceiver 1810 can also use a steerable nullantenna for most architectures.

FIG. 19 illustrates the possibility of using specialized antennaearchitectures. Impulse radios 1902, 1904, 1906 and 1908 of thisarchitecture may use a difference antenna analogous to the phasedifference antenna used in GPS carrier phase surveying. The referenceradios should be time synched and the mobile radio 1910 herein cantransmit and receive. Again, it should be noted that in this, as allarchitectures, the number of radios is for illustrative purposes onlyand more than one mobile impulse radio can be implemented in the presentarchitecture.

FIG. 20 illustrates a specialized antennae architecture whereindirectional antennae are used and wherein the reference impulse radios1902, 1904, 1906 and 1908 are time synched. As with the steerable nullantennae design, the implementation of this architecture will be drivenby design requirements. Also, herein the mobile impulse radiotransceiver 1910 can be use a directional antennae.

FIG. 21 illustrates amplitude sensing architectures wherein amplitudesensing is used for tracking and positioning. Herein, reference radios2002, 2004, 2006 and 2008 are likely time-synched. Instead of measuringrange using TOA methods (round-trip pulse intervals), signal amplitudeis used to determine range. Several implementations can be used such asmeasuring the “absolute” amplitude and comparing to pre-defined look uptable that relates range to amplitude, or “relative” amplitude wherepulse amplitudes from separate radios are differenced.

In addition to position locating within an impulse radio network,impulse radios can be used to augment existing positioning systems toimprove on these systems or to broaden potential coverage areas forimpulse radio systems. FIG. 22 illustrates an impulse radio navigationaugmentation architecture for augmentation of Global Positioning Systems(GPS). Impulse radios 2204 and 2206 would be used to augment stand-aloneGPS receivers. Impulse radio measurements (range, doppler, TOA, etc.)can be used to provide both additional accuracy and better geometry inparticular cases. For example, GPS₁, 2202 might be in the clear whileGPS₂, 2208, would be in foliage. GPS₁, 2202 could provide bothdifferential GPS (DGPS) corrections and impulse measurements to GPS₂,2208 to improve GPS₂, accuracy.

FIG. 23 illustrates GPS/INS augmentation in navigation augmentationarchitectures 2300. Herein impulse radios 2304 and 2306 would be used toaugment GPS/INS (inertial navigation system) units. Impulse radiomeasurements (range, doppler, TOA, etc.) can be used to provide bothadditional accuracy and better geometry in particular cases. Hereinimpulse radio 2304 could provide impulse radio measurements to theGPS/INS 2302 to improve accuracy.

Not only GPS and GPS/INS derive benefits from integrating with impulseradios, generic navigation sensors can be augmented 2400 as well.Impulse radios 2404 can be interfaced with various navigation systemssuch as electro-optical, LORAN, LASER, LIDAR, radar, SAR, VOR, DME,magnetic compasses etc. Impulse radio measurements (range, doppler, TOA,etc.) can be used to provide additional accuracy and better geometry inparticular cases. Herein, impulse radio 2206 would communicate withimpulse radio 2404 which as mentioned is interfaced with the navigationsystem.

Using the properties associated with impulse radio technology in one ofthe aforementioned architectures and with the distance and positioningtechniques herein articulated and in the patents incorporated herein byreference, the following impulse radio mobile position locating systemand method is used in building environment 2500. Further, the system andmethod herein provides for the position locating to be mobile andcapable of locating persons in an environment such as firefighters in aburning building. Because fire departments don't know in which buildingsfires are going to occur, they must be able to implement the system onthe fly. FIG. 25 shows building 2502 where a fire or other emergency maybe taking place (an example of another emergency may be policemanknowing the locating of officers in a building with hostages). Firemen#1, 2518, in this embodiment is positioned in the upper left portion ofbuilding 2502. Fireman #2, 2504, is located on the second floor towardsthe right portion of the building 2502.

Upon arrival at the building, mobile impulse radios 2516, 2514 and 2512are positioned around the building 2502. Two of the reference radios arepositioned in pre-designated areas 2528 and 2530 that were ascertainedduring the initial setup. This enables positioning relative to thebuilding schematic and overlay. In order to get three dimensionallocating, a fourth impulse radio receiver 2506 is located non-coplanerto the rest of the impulse radios location such as on top of the firetruck ladder 2508 connected to fire truck 2510. Located inside of firetruck 2510 is a computer with monitor 2520 (shown blown up as 2522). Thecomputer with monitor has preprogrammed into it an overlay of aschematic or blue print of the building for which the fire is located. Agiven fire department is typically responsible for a given area and willhave already programmed the information in to the computer and when afire is determined to be present the address is typed in and an overlayof the building is displayed.

By using one of the of architectures illustrated above, the position offirefighter #1, 2518, and firefighter #2, 2504 can be determined. Sincebuildings and scenarios vary widely from fire department to firedepartment, the best suited architecture will be on a case by casebasis. In the current illustration, the architecture of FIG. 10 is used.Once the reference radios are set up, reference radio 2514 talks toreference radios 2516, 2512, 2506 and fireman #1, 2518 mobile impulseradio and fireman #2, 2514 impulse radio. Similarly the rest of theimpulse radios synch to each other and the fireman radios. In this case,since the fireman's 2518 and 2504 mobile impulse radios are impulseradio transceivers, they can have two way communications and can also beinterfaced with a sensor to relate information to the monitor outsidesuch as temperature or the fireman's heart rate. This is one of thetruly unique characteristics of impulse radio: the dual functionalityrelating to positioning and communications in one impulse radio.

The information can be processed in impulse radio 2512 or it can be donein computer 2522. The computer 2522 processes the information and putsthe information into displayable form by taking the blue print orschematic and positioning information and displaying the position offireman #1, 2518 as shown at 2524 and fireman #2, 2504, as shown in2526.

FIG. 26 at 2600 illustrates in a block diagram the information receivedby processor 2608 located in computer 2520. The processor 2608 receivesposition information 2602 from fireman #1, 2518, who is connected toimpulse radio #1. Processor 2608 also receives information from fireman#2, 2504, connected to impulse radio #2, wherein both impulse radiosattached to the fireman are in communication with all reference impulseradios wherein the positioning is determined. At 2600 it is illustratedthat N possible fireman can be located within the building 2502 andthere positions can also be determined. As mentioned, the processor 2608can receive information 2610 and 2614 from both fireman's impulse radiotransceivers concerning temperature where the fireman are at. Again, Ndifferent parameters can be sensed and passed to be displayed as shownat 2614.

The processor takes the above positioning and sensed information and theinformation concerning the layout of the building 2606 and displays theinformation on display 2616. Although a display is illustrated, it isunderstood that the information could be interfaced with a variety ofmonitoring devices. For example, the fireman's heart rate can bedisplayed on heart rate monitor thus determining in very severe caseswhether or not the fireman is under sever stress or even alive.

Only slight modifications to this burning building example would berequired to implement the above system in the aforementioned prisonenvironment. As with the firefighters, the prison guards would carry themobile radio with them and with the incorporation of one of the abovearchitectures can use the mobile device to communicate with othermonitoring prison guards. There would likely not be a requirement forthe reference radios to be portable as they could be hard wired andlocal AC powered. Further, the same mobile impulse radio would be usedwithin the defined reference radio area (i.e., the prison), and couldthereby provide exact location information. Also, if the prison guardwere in potential danger, an alerting means could be used and thedispatch of additional security personnel could be dispatched to thedistressed guards location immediately.

FIG. 27 illustrates the impulse radio position system and method as usedin an environment such as a DisneyLand resort. Reference impulse radiotransceivers 2702, 2704, 2706, 2708, 2710, 2712, 2714, 2716 and 2718 arepositioned for maximum coverage throughout the park and are in knownreference positions. Note the severe multipath characteristics of atheme part such as this: trees, metal rides and metal buildings. Sincethe area to be covered is not variable as in the burning buildingscenario, the reference impulse radios can be either in communicationwith each other via wired or wireless means. Depending on therequirements of the park, many of the above architectures can beutilized. For example, if the theme park desires that every child beable to be located, the requirements for long battery life andinexpensive impulse radio are required. Thus an architecture like 14Awould be a good match, where the mobile impulse radio receiver is just atransmitter (i.e., low cost and very inexpensive) and the referenceradios are all in synch (easily done if all radios are hardwired or evenif communicating via wireless impulse radio transmissions). If the themepark wanted to provide emergency personnel at the park a device thatwould show the where to go immediately and cost was less of a concern,then the architecture illustrated in FIG. 14B would be used. Herein, themobile impulse radio could provide them with their location and showthem how to get to the emergency. Also, again due to the uniqueproperties of impulse radio, communications could be accomplished withthe impulse mobile radio.

In the lost child example, stations 2720 and 2722 could be set up forlocating the child when lost. The mobile impulse radio associated withthe child and his parents is stored in the computer at the time ofissue. When lost, the parents can go to station 2720 or 2722 and informthem of the child's name and request they activate the display for thatchild. As with the burning building example, an overlay of the park isin the computer memory and provides a visual display 2724 of thelocation of the child.

FIG. 28 is flow chart of the process of child location of FIG. 27.Although the process herein is specific to a theme park, the process canalso be employed in any area that can be bound by impulse radioreference radios either alone or in conjunction with other positioningsystems such as GPS. The first step is to equip the theme park withreference impulse radios 2802. In this embodiment the radios are fixedand the positioning of them is contingent of the RF propagationenvironment of each area of the theme park. For example, if there is anarea densely populated with trees or metal buildings, placement of thereference impulse radios would be closer together. Further, setting theintegration amount of the pulses would be done based on the RFpropagation environment and the information required. If it is a highlycluttered RF environment, larger integration per data bit is required.The method of accomplishing this is articulated in the patentsincorporated herein by reference.

In step 2804, each child entering the theme park is given a mobileimpulse radio. When the child is given the radio their name isassociated with the serial number of the mobile impulse radio they aregiven. The parents or guardians can place the transmitter on the childdirectly, in a stroller, in a stuffed bear given to the child as theyenter or any other method as desired. Once the mobile impulse radio hasbeen given to the child, it is activated and begins communication withthe reference impulse radios, thereby keeping track of the position ofthe child at all time within the park 2806. For privacy concerns andissues of capacity, the display portion of the child's tracking can beset so as not to activate until a report has been received that thechild is missing or if they are no longer in the coverage area. It isnoted that the mobile impulse radio is not required to be incommunication with all reference impulse radios simultaneously, as longas it is in communication with at least one of the reference impulseradios, positioning can be determined.

In step 2808, a determination is made if the child is lost in the parkor has left the park. When the system notices that the child's mobileimpulse radio is no longer in communication with the reference impulseradios, an alert is given and last known position is displayed. Thetheme park can at that time take actions deemed appropriate. If theparent loses the child in step 2810 they can immediately go to alocation station and inform the attendants of the child's name. Uponentry of the name into the database, the position of the mobile impulseradio is given and thus the corresponding child's location. The mobileimpulse radio can be designed to be very inexpensive and therefore bethrown away after use. In step 2812, if no lost child condition exists,then the parents or guardians return the mobile impulse radio to thetheme park attendants, whereafter the transmission is deactivated andremoved from the tracking system and thrown away or batteries rechargedfor subsequent use.

While the above system assumes the mobile impulse radio position is ofconcern to other than the person or object with which it is associated,it may be the case that the person or object associated with the mobileimpulse radio is concerned with its/their location. This can beaccomplished readily by implementation of one of the architecturesherein articulated.

FIG. 29 illustrates the impulse radio position locating system andmethod in a warehouse environment 2900. In a warehouse, it is veryimportant many times to know exactly where various cargo and pallets ofthings are stored. Further, the multipath effects in a warehouse can bevery pronounced and therefore ideal for impulse radio advantages. Sinceitems may be stored for long periods of time and the synching of thereference impulse radios 2902, 2904, 2906 and 2908 can easily beaccomplished via wired or wireless means the architecture of FIG. 14Bwould be effective. In FIG. 29 each item stored 2912-2930 is associatedwith an impulse radio transmitter. Again, the impulse radio is atransmitter because long battery life is desired and the item in thiscase is assumed not to be concerned with where it is located. Incommunication with reference impulse radio 2906 is a computer 2932. Anoverlay of the warehouse is located in the computers memory along withthe relative position of the reference radios and thereby can display tothe user exactly which item is where in the warehouse.

While particular embodiments of the invention have been described, itwill be understood, however, that the invention is not limited thereto,since modifications may be made by those skilled in the art,particularly in light of the foregoing teachings. It is, therefore,contemplated by the appended claims to cover any such modifications thatincorporate those features or those improvements which embody the spiritand scope of the present invention.

1. An object location system for determining the position of an object,said object location system comprising: an RF tag to transmit a tagsignal, said RF tag being associated with said object; a plurality ofreference radios positioned at known locations, each of said pluralityof reference radios being coupled to a common clock source and includinga time counting device that is indexed at a higher frequency relative tothe frequency of the common clock and frequency-locked with said commonclock source to maintain synchronization of each said time countingdevice, each of said plurality of reference radios including a receiverto receive said tag signal; and a processor obtaining times of arrivalof said tag signal at said plurality of reference radios to determinesaid position of said object based on said times of arrival and saidknown locations of said plurality of reference radios.
 2. The objectlocation system of claim 1, wherein said processor determines saidposition of said object using one of a time-of-arrival method, a roundtrip time-of-flight method, a differential time-of-arrival method, adifferenced time-of-arrival method, an angle-of-arrival method, anabsolute signal amplitude range determination method, a relative signalamplitude range determination method, a directional antenna-basedmethod, or a beam steering method.
 3. The object location system ofclaim 1, further comprising: a reference transmitter having a knownlocation to transmit a reference signal, wherein each of said pluralityof reference radios also receives said reference signal, wherein saidprocessor also obtains times of arrival of said reference signal anddetermines said position of said object based on said times of arrivalof said reference signal and said known location of said referencetransmitter.
 4. The object location system of claim 1, wherein said RFtag and said plurality of reference radios comprise ultra widebandtechnology.
 5. The object location system of claim 1, wherein said tagsignal comprises low duty cycle pulses.
 6. The object location system ofclaim 5, wherein each of said low duty cycle pulses approaches one cycleper pulse.
 7. The object location system of claim 5, wherein each ofsaid low duty cycle pulses consists of a burst of cycles.
 8. The objectlocation system of claim 7, wherein said burst of cycles is spectrallyshaped to control bandwidth to meet at least one desired property. 9.The object location system of claim 8, wherein said at least one desiredproperty comprises at least one of out of band emissions, in-bandspectral flatness, time domain peak power, or burst off timeattenuation.
 10. The object location system of claim 1, wherein saidplurality of reference radios are in communication with each other viawired or wireless means.
 11. A method for determining the position of anobject, said method comprising the steps of: associating an RF tag withsaid object; transmitting a tag signal from said RF tag; receiving saidtag signal at a plurality of reference radios positioned at knownlocations, each of said plurality of reference radios being coupled to acommon clock source and including a time counting device that is indexedat a higher frequency relative to the frequency of the common clock andfrequency-locked with said common clock source to maintainsynchronization of each said time counting device, each of saidplurality of reference radios comprising a receiver to receive said tagsignal; obtaining times of arrival of said tag signal at said pluralityof reference radios; and determining said position of said object basedon said times of arrival and said known locations of said plurality ofreference radios.
 12. The method of claim 11, wherein said position ofsaid object is determined using one of a time-of-arrival method, a roundtrip time-of-flight method, a differential time-of-arrival method, adifferenced time-of-arrival method, an angle-of-arrival method, anabsolute signal amplitude range determination method, a relative signalamplitude range determination method, a directional antenna-basedmethod, or a beam steering method.
 13. The method of claim 11, furthercomprising: placing a reference transmitter at a known location;transmitting a reference signal from said reference transmitter;receiving said reference signal at each of said plurality of referenceradios; obtaining times of arrival of said reference signal; anddetermining said position of said object based on said times of arrivalof said reference signal and said known location of said referencetransmitter.
 14. The method of claim 11, wherein said RF tag and saidplurality of reference radios comprise ultra wideband technology. 15.The method of claim 11, wherein said tag signal comprises low duty cyclepulses.
 16. The method of claim 15, wherein each of said low duty cyclepulses approaches one cycle per pulse.
 17. The method of claim 15,wherein each of said low duty cycle pulses consists of a burst ofcycles.
 18. The method of claim 17, further comprising: spectrallyshaping said burst of cycles to control bandwidth to meet at least onedesired property.
 19. The method of claim 18, wherein said at least onedesired property comprises at least one of out of band emissions,in-band spectral flatness, time domain peak power, or burst off timeattenuation.
 20. The method of claim 11, wherein said plurality ofreference radios are in communication with each other via wired orwireless means.